1. Field of the Invention
The invention relates to passive drive motors, and more particularly to passive fans.
2. Description of the Related Art
Referring to FIG. 1, a conventional fan 1 comprises a stator 11, a rotor 12, a base 13, and an impeller 14. The stator 11 is disposed on the base 13. When the rotor 12 is subjected to application of an electric current to interact with the rotor 12, the rotor 12 and impeller 14 can rotate with respect to the base 13, generating a wind force effect.
To increase a wind amount of the conventional fan 1, the area of blades of the impeller 14 is increased. Namely, the conventional fan 1 has a large size. Nevertheless, there are some drawbacks for the conventional fan 1 with the large size.
When the weight of the blades of the impeller 14 is increased, the weight of the rotor 12 is increased correspondingly. Thus, a drive device with a large size is needed to provide a required torque. However, the entire conventional fan 1 becomes bulky and manufacturing costs thereof are increased.
Moreover, when the conventional fan 1 with the large size is operated, the rotational speed thereof is limited and the drive device thus cannot be operated with optimal efficiency. Meanwhile, power consumption of the conventional fan 1 with the large size is increased, thereby resulting in waste of power.
Hence, there is a need for a passive drive motor in which only a small drive device is required to drive a large loading mechanism or a large impeller to rotate, such that power consumption is reduced and energy efficiency is enhanced.